Sometimes men need you to just leave them alone. If they are struggling with something, they won’t say it out loud or seek advice and help; instead they will retreat to their man cave and deal with their problems on their own.
If you insist on finding out what is bothering him, you are going to pressure him even more, which will make him close-up completely.
Don’t worry, you will find out what is happening because he will come to you first but only when he is ready.
Don’t push him into doing anything because you will get the opposite of what you want.